Attaching the breastcollar strap to the waterhook is a show ring thing meant to "clean up" the neck of the horse, not for the comfort of the horse. Those harnesses are (or should be) designed to accept the angle of the breastcollar strap from the breastcollar itself. Your average pleasure harness should not be tacked up this way, as it will "pull funny" on the breastcollar.
The exception is that there are some harnesses that have a strap that runs from the breastcollar strap to the waterhook, so that the breastcollar strap stays in place. I have not found that I needed that strap on my horses though.
Myrna